The present disclosure relates to a static eliminating device eliminating a static charge remained on a surface of a photosensitive drum and an image forming apparatus including this static eliminating device.
In an electrographic image forming apparatus, in order to reduce a transfer memory image occurred by a static charge remained on a surface of a photosensitive drum after a toner (a developer) is transferred, a static eliminating device irradiates the surface of the photosensitive drum with a static elimination light after the toner transfer to eliminate the static charge from the surface of the photosensitive drum.
The static eliminating device is often arranged between a charging device and a cleaning device removing adhesive, such as the toner, remained on the surface of the photosensitive drum after the toner transfer. Therefore, if rotating speed of the photosensitive drum is increased due to acceleration of the image forming apparatus, a time from the static elimination of the photosensitive drum by the static elimination device to next electrical charging in the charging device is remarkably shortened, and then, a carrier (static charge) trapped in a photosensitive layer may be insufficiently eliminated by the static elimination device. In such a case, next electrical charging is carried out while the carrier is remained on the photosensitive drum, and accordingly, there is a problem that a defective image called as the transfer memory image is easily occurred.
In order to solve this problem, there is an image forming apparatus configured so that the static eliminating device is positioned at an upstream side from the cleaning device in a rotating direction of the photosensitive drum to provide a wide interval from the static elimination device to the charging device, and then, to secure a sufficient time for removing the trapped carrier.
In a case where the static eliminating device is arranged at the upstream side from the cleaning device, although the static eliminating device is positioned at a downstream side from a transferring device, a toner not transferred on a sheet and a toner scattered after the transfer onto the sheet are floated near the transferring device. If such non-transferred toner or scattered toner is adhered onto alight emitting part of the static eliminating device, there is a possibility of reducing a light amount of the static elimination light.
In order to solve such a problem, in a case where the static eliminating device is arranged at the upstream side from the cleaning device in the rotating direction of the photosensitive drum, a partition member is arranged between the static eliminating device and transfer device so that the static eliminating device does not directly face to the transferring device and a conveying path of the sheet, and accordingly, adhesion of the toner onto the light emitting part is prevented.
In a case of arranging the partition member, a space between a housing supporting the static elimination device and partition member provides an optical path of the static elimination light. A part of the static elimination light is reflected by faces at the optical path side (called as reflecting faces) of the housing and partition member and progressed, and then, radiated from an opening end between the housing and partition member to the photosensitive drum. Since the light amount of the static elimination light radiating to the photosensitive drum depends upon reflectance of the reflecting faces of the housing and partition member, the light amount of the static elimination light is increased as the reflectance of the reflecting faces is heightened. In addition, since the reflectance depends upon glossiness of the reflecting faces, the reflectance is heightened as the glossiness of the reflecting faces is heightened.
When an image forming operation is continued, the non-transferred toner or scattered toner may penetrate the optical path of the static elimination light from the opening end between the housing and partition member or the other regardless of the arrangement of the partition member.
For example, in a drum unit including the charging device, cleaning device and static elimination device in a body, the static elimination device is supported by a supporting part formed in an outer face of a housing of the drum unit, in accordance with a structure of a die used for molding the housing, an opening may be formed in apart of the supporting part. In such a case, by rotation of the photosensitive drum, a wind along the rotating direction of the photosensitive drum is occurred near the surface of the photosensitive drum. Moreover, a wind path is generated so that the wind penetrates the optical path of the static elimination light from the opening end between the housing and partition member, and then, runs out from the opening formed in the supporting part. If the scattered toner penetrates the optical path along the wind path, there are problems that the penetrated toner is adhered onto the reflecting faces of the housing and partition member, and accordingly, the reflectance of the reflecting faces is decreased.
Further, since the toner amount adhered onto the reflecting faces is uneven in an axial direction of the photosensitive drum, the reflectance is remarkably decreased at a place with much toner adhesion amount and the reflectance is hardly decreased at a place with little toner adhesion amount. Therefore, the light amount of the static elimination light being radiated onto the surface of the photosensitive drum is varied in the axial direction of the photosensitive drum, and then, surface electrical potential on the photosensitive drum after the static elimination becomes uneven. As a result, there is a possibility that a defective image, such as white void in a place with high surface electrical potential, is occurred.